Conventionally, there is disclosed an exhaust purifier of an internal combustion engine in which at least a part of a harmful component in an exhaust gas from an internal combustion engine is concentrated by a concentration device, at least a part of the harmful component concentrated by the concentration device is converted into a highly reactive gas by a conversion device, and the harmful component, at least a part of which has been converted into the highly reactive gas by the conversion device, is purified by an exhaust gas purification catalyst (see, for example, Patent Literature 1). In this exhaust purifier of the internal combustion engine, the conversion device is a device that adds an oxidizing agent to the harmful component, which is concentrated by the concentration device, to oxidize at least a part of the harmful component and to convert it into a highly reactive gas. Also, the oxidizing agent is ozone, and this ozone is generated by electrolyzing water by a water electrolysis device. Here, in the water electrolysis device, hydrogen (H2) is formed along with ozone at a time of electrolysis of water. Specifically, water is decomposed on an anode side partitioned by a cation exchange membrane to generate ozone, and a hydrogen gas is generated on a cathode side from a hydrogen ion which has passed through the cation exchange membrane. Furthermore, an adsorbent is housed in the concentration device, and an ozone adding valve is provided as the conversion device in an exhaust pipe on an exhaust gas upstream side of the concentration device.
In the thus configured exhaust purifier of the internal combustion engine, the concentration device concentrates the at least part of the harmful component in the exhaust gas from the internal combustion engine. Specifically, a hydrocarbon and NOx in the exhaust gas are temporarily adsorbed onto the adsorbent housed in the concentration device, to thereby concentrate the hydrocarbon and NOx. Ozone (O3) as the oxidizing agent is injected from the ozone adding valve toward the adsorbent of the concentration device. Thereby, ozone is added to the harmful component adsorbed onto the adsorbent. At this time, at least a part of the hydrocarbon and NOx adsorbed onto the adsorbent are oxidized and converted into a highly reactive gas due to high oxidation activity of ozone. For example, among hydrocarbons, when an olefinic hydrocarbon is converted into an oxygen-containing hydrocarbon such as an aldehyde, the reactivity becomes high, and nitrogen monoxide (NO) of NOx is oxidized and converted into nitrogen dioxide (NO2), whereby the reactivity becomes high. The harmful component, the at least part of which has been converted into the highly reactive gas by the addition of ozone, is supplied to the exhaust purification catalyst on the downstream side. Then, in the case where the exhaust purification catalyst is a selective reduction catalyst, in this selective reduction catalyst, the partially oxidized hydrocarbon and nitrogen dioxide (NO2) are caused to react with each other and finally purified into carbon dioxide, water, and nitrogen.
Meanwhile, there is disclosed an exhaust gas purifier of an internal combustion engine, which is configured so that a catalyst for purifying a harmful component in an exhaust gas is disposed in an exhaust passage of the internal combustion engine; that an active oxygen supply device supplies active oxygen into the exhaust passage on an exhaust gas upstream side of this catalyst; that an unburned fuel component supply means increases the concentration of the unburned fuel component in the exhaust gas flowing through the exhaust passage on the exhaust gas upstream side of the catalyst to be higher than usual; and that in the case where an increase in temperature of the catalyst is required, not only a catalyst temperature-increasing means supplies active oxygen into the exhaust passage on the exhaust gas upstream side of the catalyst by the active oxygen supply device, but also the unburned fuel component supply means increases the concentration of the unburned fuel component in the exhaust gas flowing through the exhaust passage on the exhaust gas upstream side of the catalyst (see, for example, Patent Literature 2). In this exhaust gas purifier of the internal combustion engine, the catalyst contains Ag as a catalyst component. Also, the active oxygen supply device is configured so as to supply ozone as the active oxygen.
In the thus configured exhaust gas purifier of the internal combustion engine, in the case where an increase of the temperature of the catalyst is required, a catalyst temperature-increasing control for adding active oxygen and an unburned fuel component to the exhaust gas flowing through the exhaust passage on the exhaust gas upstream side of the catalyst can be executed. Since the active oxygen has a strong oxidation power, the added active oxygen and unburned fuel component can efficiently react with each other even from a low temperature. For that reason, the temperature of the catalyst can be rapidly increased utilizing a reaction heat thereof. Also, since the catalyst contains Ag, when the active oxygen and the unburned fuel component are added by means of the catalyst temperature-increasing control, CO is generated due to a reaction therebetween. Ag expresses activity for efficiently oxidizing CO from a low temperature in the copresence of the active oxygen. For that reason, CO generated due to the reaction between the active oxygen and the unburned fuel component, which are added during the catalyst temperature-increasing control, can be oxidized and purified while Ag acts as a catalyst.